The present invention relates to an anti-skid control system for use in an automotive vehicle, and in particular to an anti-skid control system for controlling braking force applied to road-wheels in braking operation to prevent the road-wheels from being locked.
Conventionally, there has been provided an anti-skid control system for reducing a braking distance. In the conventional anti-skid control system, the adjustment of the braking distance is attained by adjusting the braking force to be applied to a road-wheel taking into consideration the deceleration of the road-wheel, the slip rate thereof, and other factors as disclosed in Japanese Patent Laid-open Prints No. Sho 60-154947 and No. Sho 62-314554 published without examination in 1985 and 1987, respectively. In the conventional anti-skid control system, an initiation of an anti-lock control is established when a speed of the road-wheel is decreased relative to a target vehicle speed, or a deceleration of the road-wheel is increased relative to a target vehicle deceleration.
Sometimes, upon a jumping motion or a turning motion of the vehicle, the road-wheel may move away from the road surface, which will bring a temporary decrease of the load applied to the road-wheel. In general, the less the load is applied to the road-wheel, the more the road-wheel is apt to be brought into locked condition. If any one of such situations occurs, due to the decrease of the load, the road-wheel is apt to be locked, thereby increasing the slip rate thereof. Thus, the decrease of the speed of the road-wheel relative to the vehicle-speed, the increase of deceleration of the road-wheel relative to the vehicle-speed will establish an initiation of the anti-skid control. The anti-skid control system decreases the braking pressure for the prevention of the locked condition of the road-wheel. Thereafter, if the load recovers as it was, depending on this recovery, the braking pressure is also increased. However, it takes a time for the recovery of the braking pressure as it was, which brings an early initiation of the anti-skid control resulting in the prolongation of the braking distance.